Ventricular assist devices ("VAD"), based on sealless rotary blood pumps, do not have drive shafts for the transmission of torque. Transmission of torque can readily be accomplished with the use of magnetic or electromagnetic coupling, but supporting the impeller poses challenges because of the unique properties of blood.
Blood can be used for hydrodynamic support and surface lubrication in sealless rotary pumps. But, the use of blood for lubrication poses many challenges not encountered with conventional lubricants such as oil, graphite, etc. Blood is composed of cellular elements which can be adversely effected or destroyed by mechanical forces and heat. In addition, blood carries large molecules, such as proteins, enzymes and clotting precursors, which can be damaged, denatured or inactivated as a result of heat, shear, material surfaces, or bearing clearances found in rotary blood pumps. Also, the blood can form clots.
Thus, the use of blood for hydrodynamic support and surface lubrication imposes a very narrow range of operating conditions. To avoid cell injury, only very low levels of shear can be produced. To avoid protein denaturation, local heats must not exceed 45 degrees C. To avoid the formation of clots, surfaces must be made of blood compatible materials and rapid exchange of blood within narrow clearances must be ensured.
Accordingly, it is an object of the present invention to provide a rotary blood pump using hydrodynamic bearings, magnet bearings, hybrid hydrodynamic/magnetic bearings or combinations thereof.
It is yet a further object of the present invention to provide a rotary blood pump in which all the internal surfaces are regularly washed by fresh blood to prevent thrombosis from occurring.
It is another object of the present invention to provide a rotary blood pump which does not subject any blood to shear forces, temperatures or materials that would substantially damage blood or adversely react with blood.
It is another object of the present invention to provide a rotary blood pump in which the magnetic and hydrodynamic forces acting on the rotor provide sufficient support to allow elimination of the shaft.
Other objects and advantages will become apparent as the description proceeds.